AP Biology Test #3b - Meiosis And Mendelian Genetics

The individual shown in the image most likely suffers from Down's syndrome. This genetic disorder is caused by the presence of an extra copy of chromosome 21. Individuals with Down's syndrome typically exhibit distinct physical features such as almond-shaped eyes, a flat facial profile, and a protruding tongue. They may also experience developmental delays, intellectual disabilities, and have an increased risk of certain health conditions.

Normal human males develop from fertilized eggs containing the sex chromosome combination XY. This means that they inherit one X chromosome from their mother and one Y chromosome from their father. The presence of the Y chromosome triggers the development of male characteristics during embryonic development.

The diploid number of chromosomes in a human skin cell is 46, meaning it contains two sets of 23 chromosomes. However, a human ovum (egg) is a haploid cell, meaning it only contains one set of chromosomes. Therefore, the number of chromosomes found in a human ovum is 23.

Trisomy is a mutation that occurs when an individual has an extra chromosome. Chromosomes are structures found in the nucleus of cells that contain DNA. Each chromosome carries many genes, which are segments of DNA that provide instructions for the production of proteins. Mutations in chromosomes can lead to genetic disorders, and trisomy specifically refers to the presence of an additional chromosome in a cell. Therefore, the correct answer is chromosome.

When two parents with genotype Aa (heterozygous) reproduce, there is a 1/2 probability for each parent to pass on the "A" allele and a 1/2 probability to pass on the "a" allele. Therefore, the probability of producing the genotype Aa is 1/2.

A karyotype is a visual representation of an individual's chromosomes, arranged in pairs according to size, shape, and banding pattern. It allows for the identification of any chromosomal abnormalities or genetic disorders. The other options, centromere and centrosome, are specific structures within a chromosome and a cell, respectively. Amniocentesis, on the other hand, is a prenatal procedure to collect and analyze the amniotic fluid for genetic abnormalities. Therefore, the correct answer is karyotype.

Gametes are reproductive cells (sperm and eggs) that contain half the number of chromosomes found in other cells of the body. In humans, each cell normally contains 23 pairs of chromosomes, with one pair being the sex chromosomes (XX in females and XY in males). Therefore, gametes contain only one chromosome from each pair, resulting in 22 autosomes (non-sex chromosomes) and 1 sex chromosome.

Crossing-over occurs during prophase I of meiosis. This is the stage where homologous chromosomes pair up and exchange genetic material through a process called crossing-over. This genetic exchange results in new combinations of alleles and increases genetic diversity. The other options (prophase II, fertilization, and at the centromere) are not correct because crossing-over specifically occurs during prophase I.

When the parents have genotypes Rr and rr, there is a 50% chance that the offspring will inherit the R allele from the Rr parent and a 50% chance that it will inherit the r allele from the rr parent. Therefore, there is a 1/2 or 50% probability that the genotype Rr will be produced.

If 2n = 48, it means that the cell has 48 chromosomes in total. During meiosis, the cell undergoes two rounds of division, resulting in four daughter cells. Each daughter cell will have half the number of chromosomes as the parent cell. Therefore, the chromosome number in each cell after meiosis would be 48/2 = 24.

When crossing two rabbits with the genotype AaBb, there are four possible combinations of alleles that can be inherited by the offspring: AB, Ab, aB, and ab. The question asks for the probability of the offspring having the genotype aabb, which means both alleles for hair length (a) and color (b) must be inherited from both parents.

Since each parent has one allele for hair length (Aa) and one allele for color (Bb), the probability of passing on the allele for short hair (a) and brown color (b) is 1/2 for each parent.

To calculate the probability of both parents passing on these alleles, we multiply the probabilities together: (1/2) * (1/2) = 1/4.

Since there are two parents, we multiply the probability by 2: (1/4) * 2 = 1/8.

However, the question asks for the probability of the offspring having the genotype aabb, which means both alleles for hair length (a) and color (b) must be inherited from both parents.

To calculate this, we multiply the probability again: (1/8) * (1/8) = 1/64.

Therefore, the probability of the cross AaBb X AaBb producing offspring with the genotype aabb is 1/64, which is equivalent to 1/16.

Red-headed people frequently having freckles suggests that the genes for these two traits are linked on the same chromosome. This means that the genes responsible for red hair and freckles are physically close to each other on the same chromosome, making them more likely to be inherited together.

Homologous chromosomes are pairs of chromosomes that have the same genes in the same loci, although they may have different alleles. They are inherited from each parent and carry genetic information for the same traits. Therefore, the correct answer is "same traits."

Based on the information provided, the pedigree chart shows the genetic trait in a pattern consistent with autosomal recessive inheritance. This means that the trait is caused by a set of alleles located on autosomal chromosomes (non-sex chromosomes) and both copies of the gene must be mutated in order for the trait to be expressed. This is supported by the presence of affected individuals who have unaffected parents, indicating that they inherited one copy of the mutated allele from each parent.

Sickle cell anemia is a genetic disorder that affects the shape of red blood cells. The abnormal hemoglobin molecules in sickle cell anemia cause the red blood cells to become rigid and sickle-shaped, which can lead to poor circulation. This can result in symptoms such as fatigue, shortness of breath, and pain in the joints and chest. Sterility in females, failure of the blood to clot, and failure of chloride ion transport mechanism are not directly associated with sickle cell anemia.

The parents have the genotype CcDd, which means they each have one copy of the recessive allele for both traits. In order for the genotype ccdd to be produced, both parents must pass on their recessive alleles for both traits. The probability of passing on a recessive allele for each trait is 1/2. Since there are two traits, the probability of passing on the recessive alleles for both traits is (1/2) * (1/2) = 1/4. The probability of both parents passing on the recessive alleles for both traits is (1/4) * (1/4) = 1/16. Therefore, the probability of the genotype ccdd being produced is 1/16.

Segregation of alleles refers to the separation of different forms of a gene during the formation of reproductive cells. This process is essential for genetic diversity and inheritance. In flowering plants, insects, flatworms, and ferns, segregation of alleles occurs during meiosis, ensuring the mixing and shuffling of genetic material. However, bacteria reproduce asexually through binary fission, which does not involve meiosis or the segregation of alleles. Therefore, bacteria do not undergo the process of allele segregation.

The sperm cell in most vertebrates contributes a haploid complement of chromosomes to the new organism. This means that it provides half of the genetic material needed for the formation of the zygote, which will develop into a new organism. The other half of the genetic material is contributed by the egg cell. This combination of genetic material from both parents ensures genetic diversity in the offspring.

The genotype TTSs can only be produced if both parents contribute the recessive allele for the first gene (Tt) and the dominant allele for the second gene (Ss). Since the parents have the genotypes TTSs and TtSS, there is a 1/2 chance that each parent will contribute the recessive allele for the first gene. Additionally, there is a 1/2 chance that each parent will contribute the dominant allele for the second gene. Therefore, the probability of both events occurring is 1/2 * 1/2 = 1/4.

The relative position of the four genes on the chromosome can be determined based on the crossing over frequencies. The highest crossing over frequency is observed between genes C and D (50%), indicating that they are the farthest apart on the chromosome. The next highest crossing over frequency is between genes C and B (45%), suggesting that they are the second farthest apart. The crossing over frequency between genes A and B is 30%, indicating that they are closer together than genes C and B. Finally, the lowest crossing over frequency is observed between genes B and D (5%), suggesting that they are the closest together. Therefore, the correct relative position of the genes on the chromosome is CABD.

Polygenic inheritance refers to the inheritance of a trait that is controlled by multiple genes. In the case of skin color in humans, it is influenced by the combined effects of several genes. Each gene contributes a small amount to the overall variation in skin color, resulting in a continuous range of shades. This is why skin color does not follow a simple dominant-recessive pattern and can vary widely within populations. Therefore, the correct answer is polygenic inheritance.

Meiosis is a type of cell division that occurs in reproductive structures of mammals and leads to the production of cells with the haploid number of chromosomes. It serves as a factor in bringing about variation among offspring by shuffling and recombining genetic material. It follows DNA replication, as the DNA is first replicated before undergoing meiosis. However, the statement that it produces four genetically identical gametes is incorrect. Meiosis actually produces four genetically unique gametes due to the process of crossing over and independent assortment, which further increases genetic variation among offspring.

A Barr body is formed when one of the X chromosomes in the cells of females is randomly inactivated during early development. This inactivation process ensures that the genes on the X chromosome are expressed in a balanced manner between males and females. The inactivated X chromosome condenses into a dense structure known as a Barr body, which can be observed in the nucleus of cells. This inactivation of one X chromosome allows for equal gene expression between males (who have one X chromosome) and females (who have two X chromosomes).

When crossing two individuals with the genotype AaBb, there are four possible combinations of alleles that can be passed on to the offspring: AB, Ab, aB, and ab. Since we are interested in the genotype Aabb, we need to consider the combination of alleles Ab and ab. Each of these combinations has a 1/2 probability of occurring. To get the genotype Aabb, we need the combination Ab from one parent and ab from the other parent. Since these events are independent, we multiply the probabilities together: 1/2 * 1/2 = 1/4. However, we need to consider that this combination can occur in two different ways: Ab from the first parent and ab from the second parent, or ab from the first parent and Ab from the second parent. Therefore, we multiply the probability by 2: 1/4 * 2 = 1/8. Hence, the probability of producing offspring with the genotype Aabb is 1/8.

When individuals with blood type AB and type O have offspring, the possible blood types of the offspring can be A or B. This is because blood type A and B are dominant over blood type O, and blood type O is recessive. Therefore, if one parent has blood type AB (which is a combination of A and B) and the other parent has blood type O, their offspring can inherit either blood type A or B.

The pedigree chart is not provided, so it is not possible to examine it. Therefore, an explanation cannot be generated.

The exchange of segments of DNA between the members of a pair of chromosomes acts as a source of variations within a species. This process, known as genetic recombination or crossing over, occurs during meiosis when homologous chromosomes pair up and exchange genetic material. This exchange leads to the creation of new combinations of alleles, increasing genetic diversity within a population. These genetic variations can be beneficial, allowing individuals to adapt to changing environments and increasing the chances of survival and reproduction. Therefore, the exchange of DNA segments is not only essential for species' evolution but also prevents genetic stagnation.

When a vermillion-eyed female is crossed with a wild-type male, all the male offspring will have vermillion eyes. This is because the vermillion eye trait is sex-linked recessive, meaning it is carried on the sex chromosome. Females have two X chromosomes, so they can carry a dominant wild-type allele on one X chromosome and a recessive vermillion allele on the other. However, males have one X and one Y chromosome, so if they inherit the vermillion allele from the female, they do not have another X chromosome to potentially carry a dominant wild-type allele. Therefore, all male offspring from this cross will inherit the vermillion eye trait.

The probable genotype of individual II-4 is NN or Nn because the question does not provide any information about the genotype of individual II-4. However, since the question states "probable genotype," it suggests that there is a possibility of either NN or Nn genotype for individual II-4.

Based on the given pedigree, we can determine that both parents (II-7 and II-8) are carriers of the recessive gene for albinism (Nn). The probability of passing on the recessive gene to their child is 1/2. Additionally, the probability of the child being male is 1/2. Therefore, the probability of the next child being a male with albinism is (1/2) * (1/2) = 1/4.

The probability of an offspring having the genotype AABbCcDd can be determined by multiplying the individual probabilities of inheriting each allele. In this case, AABbCcDd is the result of inheriting the Aa, Bb, Cc, and Dd alleles from both parents. Since each parent has two alleles for each gene, the probability of inheriting the Aa allele from the first parent is 1/2, the probability of inheriting the Bb allele from the first parent is 1/2, and so on. Multiplying these probabilities together gives (1/2) * (1/2) * (1/2) * (1/2) = 1/16. Therefore, the correct answer is 1/16.

The given ratios of coat colors in the offspring suggest that the white coat color is expressed as a result of epistasis. Epistasis occurs when one gene masks or modifies the expression of another gene. In this case, it is likely that a gene at a different locus is controlling the expression of the white coat color gene, resulting in the observed ratios of coat colors in the offspring.

Polar bodies are small, non-functional cells that are produced during oogenesis in females. They are formed as a result of an unequal division of cytoplasm during meiosis. The purpose of polar bodies is to discard excess cytoplasm and provide the maximum amount of cytoplasm and resources to the ovum or egg cell. This ensures that the ovum has enough nutrients and resources to support fertilization and early embryonic development. Therefore, the statement "It provides the maximum amount of cytoplasm and resources to the ovum" is true about the production of polar bodies in humans.

The correct answer is nn and Nn. This is because the offspring's genotype includes a lowercase "n" allele, which indicates that one of the parents must have had the genotype "nn". Additionally, the offspring's genotype also includes an uppercase "N" allele, indicating that the other parent must have had the genotype "Nn".

In prophase of mitosis, a human cell will have the same number of chromosomes as in the parent cell, whereas in prophase l of meiosis, the cell will have half the number of chromosomes as in the parent cell. This is because meiosis involves two rounds of cell division, resulting in the formation of four haploid cells, each with half the number of chromosomes. Therefore, the presence of twice as many chromosomes in the meiotic cell distinguishes it from a cell in prophase of mitosis.